The present invention relates to the art of rolling cone cutter earth boring bits and, more particularly, to a rolling cone cutter earth boring bit with improved means for sealing the bearings of the bit from the abrasive materials in the borehole and retaining lubricant within the bearing area.
A rolling cone cutter earth boring bit consists of a main bit body adapted to be connected to a rotary drill string. The bit includes individual rotatable cone cutters mounted on individual bearing pins extending from the main bit body. Bearing systems are provided between the cone cutters and the bearing pins to promote rotation of the cutters and means are provided on the outer surface of the cone cutters for disintegrating the earth formations as the bit and the cutters rotate. A sufficient supply of uncontaminated lubricant should be maintained proximate the bearing systems throughout the lifetime of the bit. Various forms of seals have been provided between the cone cutters and the bearing pins upon which they are mounted to retain lubricant and prevent contamination; however, the need for new sealing systems is as acute today as any time in the history of rock drilling.
A rolling cone cutter earth boring bit must operate under very severe conditions, and the size and geometry of the bit is restricted by the operating characteristics. At the same time, a longer lifetime and improved performance is needed from the bit. In attempting to provide an improved bit, new and improved materials have been developed for the cutting structure of the cone cutters. They have provided a longer useful lifetime for the cone cutters. This has resulted in the bearing systems of the bit being often the first to fail during the drilling operation. Consequently, a need exists for new and improved bearing systems to extend the useful lifetime of the bit and to allow development of other elements that interact with the sealing and bearing systems. In attempting to improve the bearing systems, various seal systems have been provided to maintain the bearing area free of harmful materials and retain lubricant. In attempting to provide new sealing systems, great care must be taken that the overall capacity of the bearing systems is not reduced.
In order to more fully appreciate the problems involved in providing new sealing systems for rolling cone earth boring bits, the following factors should be borne in mind. An entirely effective system for sealing bit bearings (especially with non-friction elements such as balls and rollers) has, to date, eluded designers. Relatively loose manufacturing tolerances inherently necessary in such bearing assemblies create sealing problems that have not been satisfactorily solved. The required manufacturing tolerances preclude effective use of the many common shaft sealing methods due to the limited ability of shaft seals to accept loose radial fits while still maintaining an effective sealing condition. Bit designers have thus limited non-friction bearing sealing methods to face type seals, usually of the rubber coated belleville spring urged type since this type consumes a minimum of space. However, this rubber coated spring has been only moderately successful because the rubber sealing element is subject to rapid deterioration both through friction heating and through abrasion from exposure to the very deleterious environment encountered in oil well or blast hole drilling operations. Some single element elastomer urged metal-to-metal arrangements have been tried but these have generally met with poor success since one of the mating metal faces has to be incorporated into the arm or cone of the rock bit and the necessary highly finished lapped surfaces create special problems that the rock bit manufacturer cannot solve economically.
Thus is can be seen that, to date, face type seals have not provided the long life and sealing efficiency necessary for non-friction bearings. A result has been that bit designers have opted to switch to high accuracy tight fitting friction type journal bearings using shaft seals such as rubber O-rings, and with these they have had a relatively high degree of success but only in areas where proper cooling, such as a circulating liquid, can be supplied to the bit exterior environment. In blast holes where air is the circulating media, cooling around the body of the bit is not adequate to allow use of friction type bearings and when these sealed and lubricated friction bearing bits are used in a blast hole application, the bit soon heats up to an intolerable extent causing the elastomers in the seals to fail, followed quickly by failure of the bit bearings.
Designers of blast hole bits have continued using non-friction bearings in blast hole bit bearing assemblies because of the foregoing considerations. Since it is desirable that these bearings be fitted with a maximum size and quantity of rolling elements to withstand the very heavy loads imposed while at the same time yielding to the hole size limitations specified by the user, a classic designers dilemma of adapting a maximum capacity bearing in a minimum of space is produced. This dilemma invariably leads to compromises which circumvent many of the well known requirements for proper assembly and use of high precision non-friction rolling elememt bearings. Normal basic requirements, such as provisions for preload adjustments are considered impractical in rock bit bearings due to space limitations. Thus the blast hole rock bit designer compromises his instinctive desire for high precision guided element bearings to the reality of his need for maximum capacity (i.e., maximum possible quantity of ball and roller elements consistent with his special constraints) requiring him to accept a tolerance build-up across the bearing races of ten to twelve thousandths of an inch. This tolerance accumulation though reasonable, is still far too much for effective operation of many forms of shaft seals.